DESCRIPTION: (Applicant's abstract) Learning how axons of retinal ganglion cells grow from their origins in the retina to their targets in the brain is an important goal for understanding how the visual system develops. A number of cell adhesion molecules (CAMs) have been found in the optic fiber layer and optic nerve and are thought to be important in axon growth and guidance. We have found that one CAM, called L1 (also referred to as NILE, Ng-CAM, 8D9 or G4), is present on axon of retinal ganglion cells and is a potent substrate for growth of axons of retinal ganglion cells in vitro. Moreover, preliminary experiments suggest that L1 may be able to support axon regeneration in the adult nervous system. The experiments described in this proposal will provide important new information about how L1 participates in visual system development and will extend our knowledge about how CAMs can function to promote and guide axon growth following damage to the visual system. Biochemical, immunological and molecular biological experiments will examine how L1 binding functions in axon adhesion. In vitro experiments will investigate how L1 mediated axonal adhesion functions in guiding axons along visual pathways. In vivo experiments will evaluate the ability of purified L1 to promote axon growth in the visual system.